Single-celled, microscopic algae naturally occur in the surface layer of all aquatic environments. These plant-like organisms, known as microalgae or phytoplankton, form the base of the food web upon which nearly all other marine organisms depend. An algae bloom occurs when estuarine, marine, or fresh water algae accumulate rapidly and form dense patches that may be visible near the surface of water.
Certain species of phytoplankton contain photosynthetic pigments that vary in color from green to brown to red. When algae are present in high concentration, the water appears to be discolored or murky, varying in color from white to almost black, often being red or brown. “Red Tide” is a common name for algae blooms, however, not all algae blooms are dense enough to cause water discoloration, and not all algae blooms are red.
Algae blooms typically involve the rapid growth of a single species of phytoplankton in an area generally because of an increase in algae nutrients such as nitrogen and phosphorous. Only a small number of the thousands of species of marine phytoplankton are known to be harmful or toxic. Red Tides are often caused by a species of phytoplankton known as karenia brevis. Algae blooms of karenia brevis may occur along coastal waters. The density of these organisms during an algae bloom can exceed tens of millions of cells per liter of seawater, and often discolors the water a deep reddish-brown hue.
Harmful Algae Blooms are associated with wildlife mortalities among marine and coastal species of fish, birds, marine mammals and other organisms. These mortalities are caused by exposure to various toxins produced by harmful phytoplankton.
The dinoflagellate Alexandrium fundyense, produces saxitoxin, the neurotoxin responsible for paralytic shellfish poisoning. The dinoflagellate Karenia brevis, produces brevetoxin, the neurotoxin responsible for neurotoxic shellfish poisoning. Brevetoxin, a potent neurotoxin, has been known to kill even large mammals such as bottlenose dolphins. California coastal waters also experience seasonal blooms of Pseudo-nitzschia, a diatom known to produce domoic acid, the neurotoxin responsible for amnesic shellfish poisoning.
Phytoplankton toxins become concentrated in filter feeding marine organisms when they consume large quantities of toxic plankton. These filter feeders include shellfish, finfish, baleen whales, crustaceans and benthic invertebrates. Mussels, clams, oysters, and abalones collected in areas affected by algae blooms can be dangerous for human consumption, leading to closure of shellfish beds for harvesting. Toxic algae blooms cause millions of dollars of damage annually to sea food producing communities and to the farmed sea food industry.
Generally an increase of nutrients, such as nitrogen and phosphates, in an aquatic environment promotes the rapid growth of simple algae or plankton. The rapid growth of algae and plankton, however, is unsustainable. Oxygen depletion of the water column (hypoxia) can occur from excessive phytoplankton respiration. The eventual die-off of the algae and their resulting degradation by bacteria may cause anoxia, a condition in which the decaying algae use up dissolved oxygen causing fish and other marine animals to suffocate.
Chemical treatment of algae blooms has been attempted using copper sulfate (bluestone) and chelated copper compounds as algaecides. Such chemicals have their own restrictions and toxicity to marine animals. Besides being toxic, algaecides may indiscriminately kill off non-blooming algae essential to the eco-system. Other treatments have involved deploying powdered clay over a bloom to adsorb and sink the toxic algae. Clay treatment, however, indiscriminately kills other organisms in the environment.
Biological treatment of an algae bloom may include introducing algae eating species of fish such as grass carp or silver carp. However, introducing a non-native species of fish may be detrimental to the local eco-system and should be used with extreme caution.
Mechanically filtering an algae bloom may also be a viable treatment but requires manpower and filtering equipment.
Thus what is needed are methods and agents for treating algae blooms that are more effective and environmentally friendly. The desired agents could be deployed over sensitive eco-systems quickly and relatively inexpensively.